Hope for the Slope

October 25th, 2013

As many know, dealing with sloped ceilings in Autodesk® Revit® can be a difficult task when a family includes an annotation symbol along with 3D components. With ‘out of the box’ families, users must decide if symbology is shown correctly in plan view for accurate plans, or in section views for accurate clash detection. Because symbolic lines can only be displayed when they are parallel to the view plane, a typical face-based family on a sloped ceiling will not display the symbolic line graphics, leaving the user with no plan symbol. The 3D representation of the device/fixture is visible, yet skewed in plan view by the slope of the ceiling.

Figure 1

There are options to work around this.

Fixtures can be placed as is and noted as being located in a sloped ceiling. It works, but doesn’t provide a clean set of documents.

Model lines can be used for plan symbols instead of symbolic lines. This allows the plan symbol to appear, but it will not look the same at fixtures located in flat ceilings. Model will also appear in section views.

Fixtures can be inserted on a work plane that is parallel to the floor. This provides a correct plan symbol, but 3D representations will be inaccurate. If the fixtures moved, there is nothing to prevent the fixture from having fixtures floating in space. Typically, architects will point this out.

Create a work plane that slopes with the ceiling. This is similar to the option above except this option will keep fixtures aligned with the ceiling but the 3D representation will still be inaccurate.

In the event the project or client requires that the 2D and 3D are both accurate, here is a new option. The concept of this approach is to rotate the plan symbol to be parallel to the floor within the family. Families placed on a ceiling with a 5° slope will rotate the plan symbol 5° in the opposite direction so it is once again parallel to the floor. It will show the symbolic lines just as if they were placed on a flat ceiling. This option requires users to know the ceiling slope angle, the direction of the slope, and what kind of ceiling fixture is being hosted. Ceiling fixtures can be separated into five groups.

Fixtures that use symbols that are not drawn to scale and use generic annotations (occupancy sensors).

Fixtures that use symbols that are drawn to scale and are symmetrical (can lights).

Fixtures that use symbols that are drawn to scale and are asymmetrical (2x4 light fixtures).

Fixtures that attach to a sloped surface, but both the symbolic lines and 3D representations are parallel to the floor (pendant lights).

Fixtures that attach to a sloped surface, but both the symbolic lines and 3D representations are parallel to the floor (2x4 pendant lights).

Most of the steps are the same regardless of the fixture group. This method requires you to know the direction of the ceiling slope in order to place asymmetric fixtures correctly. This is because Revit only allows the slope of a family’s plane to be modified in one direction.

Group 1

This method is for fixtures that use symbols, are not drawn to scale, and use generic annotations such as an occupancy sensor. Start with the Generic Annotation family template and add the symbology for the device. Nest that into a face-based family and name it Lighting Device 1. Nest the Lighting Device 1 family into yet another face-based family and name it Lighting Device 2. In Lighting Device 2, create a reference plane and name it Front. Next add an angle parameter called Plan Symbol Slope.

Figure 2

Lighting Device 1, which has the Generic Annotation nested into it, needs to be set as a “Shared” family in the Family Parameters.

Note: when loading a family that contains Shared families, both the Lighting Device 1 and Lighting Device 2 families will load into the project. Consider this when naming the Lighting Device 1 family. The prefix “SA_” (Shared Annotation) helps identify what the family is for. Load Lighting Device 1 into Lighting Device 2 and insert it on the Front work plane. Create additional work planes “Left,” “Right,” and “Back” with the Plan Symbol Slope parameter. Insert Lighting Device 1 on each of these work planes. Doing this accounts for the rotation of the fixture.

Repeat this process for each type of plan symbol loaded in the family if the Label Parameter is used to quickly switch symbology based on family type. Optionally create in only one elevation and add a design line type to assist in placing this family in the correct orientation. Without this design line, if the fixture is not at the correct rotation, the family will not appear until the rotation is correct. An incorrect slope will also cause the annotation symbol not to show even with the correct rotation.

Figure 3

For this reason it is recommended that an arrow be placed in the family to match the slope direction. Draw the arrow using model lines with the <Invisible Lines> subcategory. This will prevent the arrow from showing up in sections. It will only appear when hovering over the fixture. A visibility parameter called Plan Symbol Visibility can also be applied to control the visibility of the slope arrow.

Figure 4

Next add a parameter called Annotation Visible. This parameter will be yes/no parameter and have a formula driven by the Symbol Rotation so if there is no slope, only one will appear. Apply this parameter to the Lighting Device 1 that is placed on the “Left”, “Right”, and “Back” planes. When this fixture is placed on a sloped ceiling, Revit will not show the three symbols that are not parallel to the floor.

Figure 5

Group 2

Repeat the steps for Group 1, except there is no Generic Annotation Family. Just nest Lighting Device 1 into Lighting Device 2 on all four of the reference planes and apply the visibility parameter to three of the nested families.

Group 3

Since this is not a symmetrical family, the user has to be aware of the orientation needed for the fixture. Use of the space bar to rotate the family can still result in the 3D representation being wrong. To fix this, add a parameter called “rotation” to the 3D representation family to rotate it 90 degrees.

Group 4

This is the same as Group 2, except the plan symbology is nested. The families only need to be nested into the front reference plan. To aid in the placement of this family, it is recommend that a design line type is added to assist in the placing of the family in the correct orientation.

Group 5

This group is the same as Group 4. Add the parameter called “rotation” to the 3D representation family to rotate 90 degrees. Depending on the orientation, users will also need a formula to adjust the length of the pendant steps so they touch the ceiling instead of stopping short or going too far. By calculating the distance from the stem to the center of the fixture, along with the ceiling slope, users can specify two separate lengths for the stems with a trigonometry formula.

This may seem like a lot of work, but keep in mind how many families this applies to and how often sloped ceilings or sloped structure is an issue.

These options give the best of both worlds, given limitations in Revit. Users get accurate 3D representation for modeling and coordination reviews and consistent symbols throughout the construction drawings that will also make clients happy. The examples shown are based on electrical families, but the same concepts can apply to any ceiling mounted devices.

About the Authors

Mitchell Voss

Mitchell Voss is an engineering technician for Alvine Engineering, Omaha, Nebraska. Mitchell has been working with Revit since Revit MEP 2009, primarily on the electrical side. He has been a technician in Omaha since graduating from Southeast Community College in Milford in 2000. He is a Revit Architecture 2013 Certified Professional and an AutoCAD 2013 Certified Professional.